Fish feed supplements get immune cells fit

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Tessa Louwerens

Nutritional supplements in fish feed, β-glucans, strengthen the immune system cells of fish, as PhD candidate Jules Petit discovered. That may reduce the need to give fish antibiotics and vaccinations.

Petit investigated the effect of β-glucans on the immune system of carp, one of the most important farmed fish species. He discovered that these nutritional supplements have a lasting effect on macrophages, a type of immune cell that devours pathogens like a Pacman. Macrophages that were exposed to β-glucans in vitro were better at ingesting pathogens, even quite a while after the exposure. They also produced more oxygen radicals, which act as a weapon against pathogens. It was as if the macrophages had become super-fit bodybuilders.

Petit also discovered that gut bacteria in the carp were able to digest β-glucans. ‘We saw that the bacteria produced a particular fatty acid that we know has a positive effect on the immune system in mice and that can, for example, reduce asthma symptoms.’ Further research is needed to see whether the fatty acids have a similar beneficial effect on fish.

‘At present, vaccinations and antibiotics are often used to prevent and treat infections in farmed fish,’ says Petit. ‘Vaccinations are expensive and time-consuming to develop and antibiotics lead to problems such as pollution of the environment and the development of resistance.’ β-glucans are safe and relatively cheap because they are a waste product of the bio-ethanol industry. If fish farms can use them as a targeted nutritional supplement, it could mean less need to use antibiotics or vaccinations in the future, suggests Petit.